This past week, President Obama tried to sell his new “millionaires’ tax” to the Rust Belt. “What’s great about this country is our belief that anyone can make it,” he said in Cincinnati on Thursday, praising “the idea that any one of us can open a business or have an idea that could make us millionaires.” But who are the millionaires Obama is talking about? And will a tax on them help the economy? Let’s examine a few presumptions about the man with the monocle on the Monopoly board.

1) Millionaires are rich.

Being rich has gotten more expensive. A $1 million fortune was unusual in the early 19th century. The word “millionaire” wasn’t even coined until 1827 by novelist (and future British prime minister) Benjamin Disraeli. In 1845, Moses Y. Beach, editor of the New York Sun, published a small pamphlet called “Wealth and Biography of the Wealthy Citizens of New York City.” The price of admission to Beach’s list, which was wildly popular, was a mere $100,000.

By the time the first Forbes 400 list of the richest people in America was published in 1982, the smallest fortune featured was $75 million. There has been so much wealth creation in the past 30 years — much of it thanks to the microprocessor behind modern-day fortunes such as Dell, Microsoft and Bloomberg — that only billionaires are on the list. Today, $1 million in the bank generates only about $50,000 per year in interest. That isn’t chump change, but it’s roughly equal to the 2010 median household income.

2) Millionaires think they’re rich.

“Rich,” like “poor,” is a relative term. A family living on the American median income of $50,000 a year might think that one living on $500,000 is rich. But that second family, which probably knows families far better off than they are, thinks that you need $5 million a year to be truly rich, and so on.

On Thursday, 44 percent of people voting in an online survey as part of the GOP debate coverage said that a $1 million annual income made a person “rich.” In a 2008 survey of affluent Chicago households, only 22 percent thought a nest egg of $1 million was rich. In March, four out of 10 millionaires surveyed by Fidelity Investments said they do not feel rich. That same month, a majority of investment advisers surveyed in a Scottrade poll said that $1 million isn’t enough for retirement.

Though the average American family is rich beyond the wildest dreams of the average family in Bangladesh, where per capita income recently rose above $700, it’s not much compared with those who summer on beachfront properties in the Hamptons. When John D. Rockefeller learned in 1913 that the late J.P. Morgan had left an estate of $60 million, including a fabulous art collection, he reportedly said: “And to think — he wasn’t even rich.”

3) Millionaires pay proportionately

less income tax than poorer people.

In a speech on Monday, Obama said raising taxes on millionaires isn’t class warfare, but “math.” His math may be off: According to the IRS, those with adjusted gross incomes of more than $1 million paid an average of 23.3 percent in federal income taxes in 2008; those earning between $100,000 and $200,000 paid 12.7 percent; and those earning between $50,000 and $100,000 paid 8.9 percent. Half of American families don’t make enough money to pay income taxes at all.

Why do people think millionaires pay less? One cause of confusion is that stock dividends and capital gains in their bracket are taxed at a maximum of 15 percent, while regular income is taxed at a maximum of 35 percent. The rich often earn more dividend and capital gains income than regular income, so it’s tempting to wrongly conclude, as Warren Buffet has, that millionaires “wouldn’t mind being told to pay more in taxes.” But dividends are paid out of corporate profits that have already been taxed. So Buffet’s equity earnings are doubly taxed: He pays 35 percent at the corporate level and 15 percent on his own return.

4) Millionaires share the same political beliefs.

That might have been true in pre-revolutionary France, where the nobility was exempt from most taxation (and why so many were subject to a brief meeting with Dr. Guillotin’s lethal invention). But it is certainly not true in 21st-century America, where political opinions among the rich are just as diverse as they are among the less well-off.

Just consider George Soros and the Koch brothers. They are listed high on the Forbes 400 list, but Soros funds Democratic campaigns, while the Kochs helped foment the tea party revolution. Income can’t be used to predict political opinion. In 2008, for example, Obama won the votes of 60 percent of those with a family income under $50,000 and 52 percent of those earning more than than $200,000. McCain carried the middle class.

In America, millionaires have always had the freedom to disagree — even in the White House. Franklin Roosevelt, called one of the 10 richest presidents by Forbes in 2010, was denounced as a traitor to his class for instituting the New Deal. Also on Forbes’ list: famous trust-buster Theodore Roosevelt and John F. Kennedy, who proposed a “War on Poverty” days before he was assassinated.

5) Obama’s “millionaires’ tax”

won’t seriously limit investment.

That’s the line of reasoning that the administration is using. Last week, Treasury Secretary Timothy Geithner told reporters that the president’s plan wouldn’t hurt growth. “I am very confident that the modest changes we’re suggesting in terms of revenues ... would make the economy stronger in the long term, not weaker in the long term,” he said.

Geithner’s confidence is somewhat misplaced. According to a 2001 congressional study that confirmed a basic tenet of macroeconomics, “each $1 of marginal tax rate cuts would save the private economy at least $1.25 as deadweight losses fall and economic efficiency increases.” Taxes distort investment decisions. Why throw money into productive assets — those that create income through the production of wealth, such as corporate securitiesor a rental property — if the income they generate will be taxed away?

Taxes on the rich are taxes on people who create jobs. And jobs are an unalloyed good thing for an economy. Excessively taxing the capital that makes the economy go is poor public policy. And we have a recent example of how the opposite works well: Unemployment declined by a third in the four years after the Bush tax cuts were fully implemented in 2003, dropping to 4.2 percent from 6.2 percent. Meanwhile, federal revenue increased 44 percent in those years. If these tax cuts put people to work and generated money for the government, shouldn’t Obama consider the possibility that tax increases should be avoided?

John Steele Gordon is the author of “An Empire of Wealth: The Epic History of American Economic Power.” This column was written for the Washington Post.